Human cytomegalovirus (HCMV), a β-herpesvirus, is a ubiquitously occurring pathogen. In an immunocompetent person, HCMV infection is normally unnoticed, having at most mild and nonspecific symptoms. By contrast, certain risk groups, for example in immunosuppressed patients such as AIDS patients or transplant recipients, and after prenatal infection, HCMV infection has serious manifestations (Staras S A et al., 2006 Clin Infect Dis 43(9):1143-51; Hebart H et al., 2004 Hum Immunol 65(5):432-6; Rowshani A T et al., 2005 Transplantation 79(4):381-6). Existing therapies include the use of immunoglobulins and anti-viral agents such as ganciclovir and its derivatives, which are most effective when used prophylactically or very early during infection in at risk populations. However, existing therapies are characterized by significant toxicity and limited efficacy, especially for late-onset disease (Boeckh M., 2004 Pediatr Transplant 8(Suppl. 5):19-27; Limaye A P., 2004 Transplantation 78(9):1390-6), and they have not had an impact on congenital HCMV disease. Development of an effective vaccine to protect against HCMV disease is recognized as an important public health priority (Arvin μM et al., 2004 Clin Infect Dis 39(2):233-9).